Bicycle rear sprocket assembly

ABSTRACT

A bicycle rear sprocket assembly has a sprocket carrier, a first sprocket, a second sprocket and a third sprocket. The first and second sprockets are attached to opposite axial sides of the outer end portion of the attachment member of the sprocket carrier using a common fastener that extends through the first and second attachment portions and the outer end portion of the attachment member. The third sprocket is disposed on adjacent the second sprocket. The second sprocket has a free edge spaced radially inwardly from the common fastener by a distance at least as large as one-half of a maximum transverse dimension of the fastener measured in a direction perpendicular to the rotation axis. At least one space maintaining projection extends axially toward an adjacent one of the second and third sprockets.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to multiple sprocket assemblies forbicycles. More specifically, the present invention relates to a bicyclerear sprocket assembly that is configured to minimize bending of andmaintain proper spacing between the sprockets.

2. Background Information

Bicycling is becoming an increasingly more popular form of recreation aswell as a means of transportation. Moreover, bicycling has become a verypopular competitive sport for both amateurs and professionals. Whetherthe bicycle is used for recreation, transportation or competition, thebicycle industry is constantly improving the various components of thebicycle to meet the demands of the riders.

In recent years, as the number of speeds available in bicycletransmissions has increased, the number of sprockets installed on therear-wheel sprocket assembly of such bicycles has increased sevensprocket wheels or more. As a result, the weight of the bicycle hasincreased. Thus, there is a desire to reduce the weight of the bicycle.In other words, in pursuit of faster running speed, it is desirable toreduce the weight of all kinds of parts of the bicycle.

In order to reduce the weight of a multiple sprocket assembly, a spider(sprocket support), which supports a plurality of ring-shaped sprocketwheels, has been used. By using a spider, a light metal such asaluminum, etc., is generally used for the spider, while various types ofsteel materials are used for the sprockets to provide adequate strength.One example of a multiple sprocket assembly that uses a spider isdisclosed in U.S. Pat. No. 6,102,821 (assigned to Shimano Inc.). In thispatent, two spiders are used with each spider supporting two sprockets.Each spider has a boss part and a plurality of support arms which extendradially outward from the outer circumferential surface of the boss partin directions perpendicular to the axis of the boss part. The sprocketsare attached to mounting surfaces on opposite side surfaces of each ofthe support arms. Accordingly, this construction is greatly improved interms of weight reduction.

However, one drawback of a multiple sprocket assembly constructed inthis manner is that if the spider is made too thin, then the sprocketmay deflect towards the adjacent sprocket. This situation can result indegrading the shifting performance of the rear derailleur. On the otherhand, if the spider is made thicker, weight of the multiple sprocketassembly increases.

In view of the above, it will be apparent to those skilled in the artfrom this disclosure that there exists a need for an improved bicyclerear sprocket assembly. This invention addresses this need in the art aswell as other needs, which will become apparent to those skilled in theart from this disclosure.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a bicycle rearsprocket assembly which is relatively lightweight, strong and resistsdeflection of the sprockets during shifting of the chain from onesprocket to the adjacent sprocket.

Another object of the present invention is to provide a bicycle sprocketassembly which is relatively easy and inexpensive to manufacture andassemble.

The foregoing objects can basically be attained by providing a bicyclerear sprocket assembly, which includes a sprocket carrier, a firstsprocket, a second sprocket and a third sprocket. The sprocket carrierincludes at least one attachment member with an inner end portion and anouter end portion disposed radially outwardly of the inner end portionrelative to a rotation axis of the sprocket carrier. The first sprocketincludes a first attachment portion and a first chain engaging portionwith a plurality of first teeth. The first sprocket is disposed on afirst axial side of the attachment member. The second sprocket includesa second attachment portion and a second chain engaging portion with aplurality of second teeth that are fewer in total number than a totalnumber of the first teeth of the first sprocket. The second sprocket isdisposed on a second axial side of the attachment member. The thirdsprocket includes a third chain engaging portion with a plurality ofthird teeth that are fewer in total number than a total number of thesecond teeth of the second sprocket. The third sprocket is disposed on asecond axial side of the second sprocket. The first and secondattachment portions are attached to the outer end portion of theattachment member using a common fastener that extends through the firstand second attachment portions and the outer end portion of theattachment member. The second attachment portion has a free edge spacedradially inwardly from the common fastener by a distance at least aslarge as one-half of a maximum transverse dimension of the fastenermeasured in a direction perpendicular to the rotation axis. At least oneof the attachment member, the second sprocket and the third sprocket hasat least one space maintaining projection extending axially towards anadjacent one of the second and third sprockets.

These objects and other objects, features, aspects and advantages of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which, taken in conjunction with theannexed drawings, discloses a preferred embodiment of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a side elevational view of a bicycle having a rear wheel witha bicycle rear sprocket assembly in accordance with a first embodimentof the present invention;

FIG. 2 is a partial cross-sectional view of the rear hub with themultiple rear sprocket assembly in accordance with the presentinvention;

FIG. 3 is an exploded, outer perspective view of the first (largest)sprocket, the first sprocket carrier and the second (second largest)sprocket of the rear sprocket assembly illustrated in FIG. 2;

FIG. 4 is an assembled, enlarged outer perspective view of the firstsprocket, the first sprocket carrier and the second sprocket illustratedin FIG. 3;

FIG. 5 is an outer axial elevational (laterally outside) view of theassembled structure illustrated in FIG. 4;

FIG. 6 is a left side (rear) elevational view of the assembled structureillustrated in FIG. 5;

FIG. 7 is a cross-sectional view of the assembled structure illustratedin FIGS. 4-6, as seen along section line 7-7 of FIG. 5;

FIG. 8 is an enlarged, partial perspective view of the structureillustrated in FIGS. 3-7, but with the first sprocket disposed adjacentthe sprocket carrier and the second sprocket spaced from the sprocketcarrier prior to attachment with the rivets;

FIG. 9 is an enlarged, perspective view of the area of the assembledstructure illustrated in FIG. 4 that is identified by the circle 9,after the first and second sprockets are attached to the sprocketcarrier with the rivets;

FIG. 10 is an exploded view of the structure illustrated in FIG. 6;

FIG. 11 is a reverse, inner perspective view of the sprocket carrierillustrated in FIGS. 3-9;

FIG. 12 is an outer axial elevational (laterally outside) view of thesprocket carrier illustrated in FIG. 11;

FIG. 13 is an inner axial elevational (laterally inner) view of thesprocket carrier illustrated in FIGS. 11 and 12;

FIG. 14 is a cross-sectional view of the sprocket carrier illustrated inFIGS. 11-13, as seen along section line 14-14 of FIG. 12;

FIG. 15 is a right side (front) elevational view of the sprocket carrierillustrated in FIG. 12;

FIG. 16 is a reverse, inner perspective view of the second sprocketillustrated in FIGS. 3-9;

FIG. 17 is an outer axial elevational (laterally outside) view of thesecond sprocket illustrated in FIG. 16;

FIG. 18 is a cross-sectional view of the second sprocket illustrated inFIGS. 16-17, as seen along section line 18-18 of FIG. 17;

FIG. 19 is an inner axial elevational (laterally inner) view of thesecond illustrated in FIGS. 16-18;

FIG. 20 is an enlarged, outside elevational view of a portion of thesecond sprocket illustrated in FIG. 17;

FIG. 21 is a reverse, inner perspective view of the first sprocketillustrated in FIGS. 3-9;

FIG. 22 is an outer axial elevational (laterally outside) view of thefirst sprocket illustrated in FIG. 21;

FIG. 23 is a cross-sectional view of the second sprocket illustrated inFIGS. 21-22, as seen along section line 23-23 of FIG. 22;

FIG. 24 is a right side (front) elevational view of the second sprocketillustrated in FIG. 22;

FIG. 25 is an inner axial elevational (laterally inner) view of thesprocket carrier illustrated in FIGS. 21-24;

FIG. 26 is a partial, outside elevational view of the third and fourthsprockets attached to the second carrier of the multiple rear sprocketassembly illustrated in FIG. 2; and

FIG. 27 is a partial, outside elevational view of the fifth and sixthsprockets attached to the third carrier of the multiple rear sprocketassembly illustrated in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Selected embodiments of the present invention will now be explained withreference to the drawings. It will be apparent to those skilled in theart from this disclosure that the following descriptions of theembodiments of the present invention are provided for illustration onlyand not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

Referring initially to FIGS. 1 and 2, a conventional bicycle 10 isillustrated having a rear bicycle hub 11 with a rear multi-stagesprocket assembly 12 mounted on a freewheel 13 in accordance with thepresent invention. The bicycle 10 basically has a frame 14 with frontand rear wheels 15 and 16 rotatably coupled thereto. A front fork 17 iscoupled between the frame 14 and the front wheel 15 in a conventionalmanner. Turning a handlebar 18, which is fixedly coupled to the frontfork 17, turns the front wheel 15. The rear wheel 16 is rotatablycoupled to a rear portion of the frame 14 via the rear hub 11. The frame14 also has a seat 19 adjustably coupled to the frame 14 and a drivetrain 20 for propelling the bicycle 10. The bicycle 10 is conventionalexcept for selected parts of the drive train 20, as discussed below.

The drive train 20 basically includes the rear multi-stage sprocketassembly 12 of the present invention, a pair of pedals 21, a frontmulti-stage sprocket assembly 22 mounted to rotate with the pedals 21,and a chain 23 extending between the rear multi-stage sprocket assembly12 and the front multi-stage sprocket assembly 22. As mentioned above,the rear sprocket assembly 12 is preferably coupled to the rear hub 11via the freewheel 13. The rear multi-stage sprocket assembly 12 in theillustrated embodiment has nine sprockets S₁-S₉ that are mounted to thefreewheel 13 of the rear hub 11 in a relatively conventional manner. Thepedals 21 are coupled to the front multi-stage sprocket assembly 22 by aconventional crank set to transfer force from the rider to the chain 23.The force from the chain 23 is then selectively transferred to the rearwheel 16 via the rear hub 11 (e.g. via the rear sprocket assembly 12 andthe freewheel 13 depending on the direction of rotation) in aconventional manner.

The drive train 20 is basically controlled by conventional front andrear shifting units (not shown) that control the lateral positions offront and rear derailleurs 27 and 28 in a conventional manner. Thus,when the rider is pedaling, the front and rear sprocket assemblies 22and 12 are rotating to circulate the chain 23 due to the movement of thepedals 21. The shifting units can be actuated by the rider to controlthe position of the front and/or rear derailleurs 27 and/or 28. Thus,when the chain 23 is circulated in the forward (clockwise direction asseen in FIG. 1), the shifting units can be actuated to control the gearratio of the drive train 20 by controlling the lateral position of thechain 23 via the derailleurs 27 and 28. The derailleurs 27 and 28selectively apply a lateral force F inwardly/outwardly to the chain 23to cause up/down shifts between the front and rear sprocket assemblies22 and 12, respectively. The drive train 20 is basically conventional,except for the rear multi-stage sprocket assembly 12. Thus, the drivetrain 20 will not be discussed and/or illustrated in detail herein,except as related to the rear multi-stage sprocket assembly 12.

Since the various parts of the bicycle 10 and most of the parts of thedrive train 20 are well known in the bicycle art, these parts of thebicycle 10 and the drive train 20 will not be discussed or illustratedin detail herein, except as they are modified in accordance with thepresent invention. Moreover, various conventional bicycle parts such asbrakes, additional sprockets, etc., which are not illustrated and/ordiscussed in detail herein, can be used in conjunction with the presentinvention.

As used herein, the terms “forward, rearward, above, below, lateral andtransverse” refer to those directions of a bicycle in its normal ridingposition, to which the rear sprocket assembly 12 is attached.Accordingly, these terms, as utilized to describe the rear sprocketassembly 12 in the claims, should be interpreted relative to bicycle 10in its normal riding position. However, the terms “down shift” and “upshift” as used herein in reference to the rear sprocket assembly 12should be interpreted to mean a shift from smaller to larger sprocketand from larger to smaller sprocket, respectively, as shown in FIG. 2.

Referring now to FIGS. 2-10, 26 and 27, the rear sprocket assembly 12 inaccordance with the present invention will now be discussed. In theillustrated embodiment, the rear sprocket assembly 12 is a nine-stagesprocket assembly with sprockets S₁-S₉ being spaced from each other atpredetermined intervals. Each of the sprockets S₁-S₉ are preferablyring-shaped members that form a continuous annular, one-piece member.The sprockets S₁-S₉ are fixedly mounted on the freewheel 13 of the rearhub 11 such that the sprockets S₁-S₉ rotate together about a center hubrotation axis X. The sprockets S₁-S₉ typically rotate together in aforward rotational direction (e.g., in a clockwise direction as viewedin FIG. 1) when the rider is pedaling in a forward (clockwise) directionto propel the bicycle 10 in a forward direction as best understood fromFIG. 1. The sprockets S₁-S₉ are preferably constructed of a lightweight,rigid material such as a metallic material. The sprockets S₁-S₉ can beconsidered first-ninth sprockets, respectively.

The rear sprocket assembly 12 is adapted to engage with the drive chain23, which is a conventional style bicycle chain as seen in FIG. 1. Thus,the drive chain 23 is a continuous loop that has a plurality of innerlink plates and a plurality of outer link plates that are pivotallyconnected to each other by articulation pins and rollers. During a chainshifting process, the chain 23 is shifted from one of the sprocket S₁-S₉to the next adjacent sprocket S₁-S₉ by the rear derailleur 28 moving thechain 23 in an axial direction relative to the axis of rotation X of thesprockets S₁-S₉.

An up shift occurs when the chain 23 is moved from a larger sprocket tothe next smaller sprocket, while a down shift occurs when the chain 23is shifted from a smaller sprocket to the next larger sprocket. Thesprockets S₁-S₉ are designed so that the chain 23 can execute smoothdown shifting and up shifting motions. Each of the sprockets S₁-S₉ has adifferent number of teeth. For instance, one example of a tooth numberarrangement for the sprockets S₁-S₉ is a 34T, 30T, 26T, 23T, 20T, 17T,15T, 13T, 11T arrangement. However, it will be apparent to those skilledin the bicycle art from this disclosure that other tooth numberarrangements are possible.

In the illustrated embodiment, the sprockets S₁-S₉ can have eitheruniform or varying thicknesses as well as uniform or varying axialspaces formed therebetween. The sprockets S₁-S₉ preferably havethicknesses between about 1.6 millimeters to about 2.2 millimeters, e.g.about 1.8 millimeters. The axial spacing between the sprockets S₁-S₉ ispreferably between about 3.6 millimeters to about 3.9 millimeters, e.g.about 3.68 millimeters. A pair of conventional spacers T are utilized ina conventional manner between the sprockets S₇-S₉ to create the optimalspacing between the sprockets S₇-S₉. Thus, the sprockets S₇-S₉ areindividual ring-shaped sprockets having internally splined openings thatare mounted directly to the freewheel 13 of the rear hub 11. On theother hand, the sprockets S₁-S₆ are mounted on sprocket carriers havingintegrated spacers such that the axial spaces between the sprocketsS₁-S₉ can be set to optimize shifting of the chain 23 therebetween.

Specifically, the sprockets S₁ and S₂ are mounted on an outer peripheryof a first sprocket carrier C₁ to form a first sprocket subassembly. Thefirst sprocket carrier C₁ creates an optimal spacing between thesprockets S₁ and S₂ as well as an optimum spacing between the sprocketsS₂ and S₃. The sprockets S₃ and S₄ are mounted on an outer periphery ofa second sprocket carrier C₂ to form a second sprocket subassemblysimilar to the first sprocket subassembly. The second sprocket carrierC₂ creates an optimal spacing between the sprockets S₃ and S₄ as well asan optimum spacing between the sprockets S₄ and S₅. The sprockets S₅ andS₆ are mounted on an outer periphery of a third sprocket carrier C₃ toform a third sprocket subassembly similar to the first and secondsprocket subassemblies. The third sprocket carrier C₃ creates an optimalspacing between the sprockets S₅ and S₆ as well as an optimum spacingbetween the sprockets S6 and S7. The sprocket carriers C₁-C₃ haveinternally splined openings that are mounted directly to the freewheel13 of the rear hub 11 in a conventional manner, as explained below. Thespacing and thickness of the sprockets S₁-S₉ can be understood from FIG.2.

Referring to FIGS. 2-10 and 21-25, the first sprocket S₁ is an annularring shaped member that basically includes a first chain engagingportion 30 a with a plurality of first teeth 30 b, and a firstattachment portion 30 c with a plurality of through holes 30 d. Thethrough holes 30 d are preferably circular shaped. The attachmentportion 30 c has a generally ring-shaped configuration with the chainengaging portion 30 a extending radially outwardly thereof. In theillustrated embodiment, the attachment portion 30 c has a plurality(i.e., five) circumferentially equally spaced attachment sections 30 e.

An inner peripheral edge 30 f of the attachment portion 30 c bulgesradially inwardly toward the rotation axis X at the attachment sections30 e. The inner peripheral edge 30 f extends axially between two opposedparallel surfaces of the attachment portion 30 c. Each of the attachmentsections 30 e preferably has one of the through holes 30 d extendingaxially therethrough adjacent the inner peripheral edge 30 f. Acircumferentially elongated weight saving cutout is preferably formed ineach attachment section in an area disposed radially between therespective through opening 30 d and the teeth 30 b. Additional, smaller(circular) weight saving cutouts are also preferably disposedcircumferentially about first sprocket S₁, as shown in FIGS. 2-10 and21-25.

Referring to FIGS. 2-10 and 16-20, the second sprocket S₂ is an annularring shaped member that basically includes a second chain engagingportion 32 a with a plurality of second teeth 32 b and a secondattachment portion 32 c with a plurality of through holes 32 d. Thethrough holes 32 d are preferably circular shaped, partially steppedthrough holes. The attachment portion 32 c has a generally ring-shapedconfiguration with the chain engaging portion 32 a extending radiallyoutwardly thereof. In the illustrated embodiment, the attachment portion32 c has a plurality (i.e., five) circumferentially equally spacedattachment sections 32 e. An inner peripheral edge 32 f of theattachment portion 32 c projects radially inwardly toward the rotationaxis X at the attachment sections 32 e to form a plurality ofrectangular shaped tabs 32 g. The inner peripheral edge 32 f extendsaxially between two opposed parallel surfaces of the attachment portion32 c. Each of the attachment sections 32 e preferably has one of thethrough holes 32 d extending axially therethrough.

The tabs 32 g are aligned with the through holes 32 d in thecircumferential direction. In other words, each tab 32 gcircumferentially overlaps one of the holes 32 d as viewed in a radialdirection along the tab 32 g (i.e. as viewed along an imaginary linepassing through the tab 32 g and the rotation axis X). The through holes32 d are preferably disposed radially outwardly of the tabs 32 g. Theinner peripheral edge 32 f has five curved sections circumferentiallydisposed between the tabs 32 g in an alternating manner. Each curvedsection has a radius of curvature smaller than the distance between thecurved section and the rotation axis X. Thus, the curved sections of theinner peripheral edge 32 f project radially inwardly in areas adjacentto the tabs 32 g. Accordingly, the holes 32 d are disposed radiallyoutwardly of the parts of the curved sections of the inner peripheraledge 32 f adjacent to the tabs 32 g.

The inner peripheral edge 32 f along the free ends of the tabs 32 g ispreferably disposed radially inwardly of the through holes 32 d by adistance D larger than a minimum diameter E of the through holes. Morepreferably, the inner peripheral edge 32 f along the free ends of thetabs 32 g is preferably disposed radially inwardly of the through holes32 d by a distance D about twice the minimum diameter E of the throughholes. In other words, the inner peripheral edge 32 f along the freeends of the tabs 32 g is preferably disposed significantly radiallyinwardly of the through holes 32 d to contribute to minimizingdeflections, as explained below. Also, the inner peripheral edge 32 falong the free ends of the tabs 32 g is preferably spaced radiallyinwardly of the through holes 32 d by a distance D larger than a radialspace between the through holes 32 d and the second roots disposedbetween the second teeth 32 b.

Referring now to FIGS. 2-15, the first sprocket carrier C, includes anannular mounting boss 34 a and a plurality of attachment members(support arms) 34 b extending radially outwardly from the mounting boss34 a in directions substantially perpendicular to the rotation axis X.Preferably, the attachment members 34 b and the mounting boss 34 a areconstructed of lightweight rigid materials such as a metallic material.The attachment members 34 b are preferably integrally formed with themounting boss 34 a as a one-piece unitary member using conventionalmanufacturing techniques such as casting and/or machining. The sprocketcarrier C₁ is preferably formed from a material having a specificgravity lower than the specific gravity of the material of the sprocketsS₁ and S₂.

The annular mounting boss 34 a has a tubular configuration with aninternally splined surface that mates with the outer portion of thefreewheel 13 in a sliding, non-rotatable arrangement in a conventionalmanner. In the illustrated embodiment, the sprocket carrier C₁ includesfive circumferentially equally spaced attachment members 34 b to form asubstantially star-shaped configuration. Each of the attachment members34 b includes an inner end portion 35 a non-movably fixed with themounting boss and an outer end portion 35 b spaced outwardly from theinner end portion 35 a. Each of the attachment members 34 b furtherincludes a cutout 35 c extending between the inner and outer endportions 35 a and 35 b. The attachment sections 30 e and 32 e of thesprockets S₁ and S₂ are attached to opposite axial sides of the outerend portions 35 b using a plurality of fasteners 36. The axial length ofthe mounting boss 34 c and the axial position of the outer end portions35 b are configured to cooperate with the freewheel 13 and the secondsprocket carrier C₂ supporting the sprockets S₃ and S₄ to provideoptimum spacing, as mentioned above.

Specifically, each outer end portion 35 b has a through hole 35 dextending between oppositely facing (parallel) axial surfaces 35 e and35 f. The axially facing surface 35 e faces in a first axial direction(laterally inwardly toward a center plane of the bicycle 10) toward thefirst sprocket S₁, while the axially facing surface 35 f faces in asecond axial direction (laterally outwardly away from the center planeof the bicycle 10) toward the second sprocket S₂ that is opposite to thefirst axial direction. The fasteners 36, such as rivets, are received inthe through holes 35 d to attach the attachment sections 30 e and theattachment sections 32 e to the outer end portions 35 b. In theillustrated embodiment, a single common fastener, such as a rivet isused to attach one of the attachment sections 30 e and one of theattachment sections 32 e to one of the outer end portions 35 b.

As mentioned above, the distance D is measured between the through holes32 d and the inner peripheral edge 32 f of the second sprocket S₂ alongthe free ends of the tabs 32 g. The distance D is at least as large asone-half of a maximum transverse dimension F of the fastener 36 measuredin a direction perpendicular to the rotation axis X. More preferably,the distance D is at least as large as the maximum transverse dimensionF of the fastener 36 measured in a direction perpendicular to therotation axis X. In the illustrated embodiment, the maximum transversedimension F of the fastener 36 corresponds to the maximum diameter ofeach of the through holes 32 d. The maximum diameter of the throughholes 32 d is measured across the recessed (stepped) section of eachthrough hole 32 d in a direction perpendicular to the rotation axis X.

In this embodiment, the sprocket carrier C₁ includes a plurality ofspace maintaining sections 34 c extending axially towards the adjacentsprocket S₃. In particular, each of the each outer end portions 35 bincludes a pair of space maintaining sections 34 c circumferentiallyspaced from each other to form a slot therebetween, which is configuredto receive one of the tabs 32 g in a mating arrangement. The pair ofspace maintaining sections 34 c of each outer end portion 35 b formparts of a space maintaining projection of each outer end portion 35 b.In this embodiment, the space maintaining sections 34 c are integrallyformed as a one-piece, unitary member with the attachment members 34 bof the sprocket carrier C₁.

Each of the space maintaining sections 34 c has a free end that isaxially spaced from the adjacent sprocket S₃ by a predetermined spacing.Preferably, the predetermined spacing is 0.1 millimeters or less. Ofcourse, the predetermined spacing can be more or less as needed and/ordesired. If the predetermined spacing becomes too large, then the amountof possible deflection of the sprockets S₁ and/or S₂ will becomegreater. Thus, it is preferable to keep the predetermined spacing assmall as possible. In fact, the predetermined spacing can be zero suchthat the free ends of the space maintaining sections 34 c contact thesprocket S₃. In this embodiment, the free ends of the space maintainingsections 34 c are disposed on opposite circumferential sides of thefasteners, which connect the sprockets S₃ and S₄ to the sprocket carrierC₂. The space maintaining sections 34 c are located radially outwardlyof the radially innermost end (the mounting boss 34 a) of the sprocketcarrier C₁.

The axial end surfaces of the space maintaining sections 34 c face inthe second axial direction. The axial end surfaces of the spacemaintaining sections 34 c are preferably located slightly radiallyinwardly of the inner peripheral edge 32 f of the second sprocket S₂along the free ends of the tabs 32 g. However, the space maintainingsections 34 c are elongated in the radial direction to form mating slotsfor receiving the tabs 32 g. Thus, the space maintaining sections 34 calso circumferentially hold the tabs 32 g, as best understood from FIGS.8 and 9.

In the illustrated embodiment, the tabs 32 g contact the axially facingsurfaces 35 f along the entire opposed surfaces of the tabs. In anycase, preferably a majority of the tabs 32 g contact the axially facingsurfaces 35 f. Thus, the inner peripheral edge 32 f of the secondsprocket S₂ along the free ends of the tabs 32 g at least partiallyoverlaps, and preferably completely overlaps, the second axially facingsurfaces 35 f as viewed in a direction parallel to the rotation axis X.Even though the tabs 32 g contact the second axially facing surfaces 35f in the illustrated embodiment, it will be apparent to those skilled inthe art from this disclosure that the tabs 32 g and the second axiallyfacing surface can be configured as opposed surfaces that do not contacteach other all of the time, i.e., which only contact each other when thesprocket S₂ begins to deflect laterally outwardly.

Referring now to FIGS. 2 and 26, the second sprocket subassembly, whichincludes the sprockets S₃ and S₄ mounted on an outer periphery of asecond sprocket carrier C₂ will now be explained. The second sprocketsubassembly has a configuration similar to the first sprocketsubassembly, which includes the sprockets S₁ and S₂ mounted on an outerperiphery of a first sprocket carrier C₁. Specifically, the sprockets S₃and S₄ are conventional annular ring shaped sprockets similar to thesprocket S₁, except for their size and number of teeth (e.g., 26T and23T, respectively). Accordingly, the sprockets S₃ and S₄ will not beexplained and/or illustrated in detail herein for the sake of brevity.However, it will be apparent to those skilled in the art from thisdisclosure that the descriptions and illustrations of the sprocket S₁also apply to the sprockets S₃ and S₄, except as explained andillustrated herein.

The sprocket S₃ is an annular ring shaped member that basically includesa third chain engaging portion 40 a with a plurality of third teeth 40b, and a third attachment portion 40 c with a plurality of through holes40 d. The through holes 40 d are preferably circular shaped. Theattachment portion 40 c has a generally ring-shaped configuration withthe chain engaging portion 40 a extending radially outwardly thereof. Inthe illustrated embodiment, the attachment portion 40 c has a plurality(i.e., five) circumferentially equally spaced attachment sections 40 ewith one of the through holes 40 d formed in each attachment section 40e. Thus, the sprocket S₃ can be attached to the sprocket carrier C₂, asexplained below.

The sprocket S₄ is an annular ring shaped member that basically includesa fourth chain engaging portion 42 a with a plurality of fourth teeth 42b, and a fourth attachment portion 42 c with a plurality of throughholes 42 d. The through holes 42 d are preferably circular shaped. Theattachment portion 42 c has a generally ring-shaped configuration withthe chain engaging portion 42 a extending radially outwardly thereof. Inthe illustrated embodiment, the attachment portion 42 c has a plurality(i.e., five) circumferentially equally spaced attachment sections 42 ewith one of the through holes 42 d formed in each attachment section 42e. Thus, the sprocket S₄ can be attached to the sprocket carrier C₂ asexplained below.

The sprocket carrier C₂ is similar to the sprocket carrier C₁. Thus, thesprocket carrier C₂ includes an annular mounting boss 44 a and aplurality of attachment members (support arms) 44 b extending radiallyoutwardly from the mounting boss 44 a in directions substantiallyperpendicular to the rotation axis X. Preferably, the attachment members44 b and the mounting boss 44 a are constructed of lightweight rigidmaterials such as a metallic material. The attachment members 44 b arepreferably integrally formed with the mounting boss 44 a as a one-pieceunitary member using conventional manufacturing techniques such ascasting and/or machining. The sprocket carrier C₂ is preferably formedfrom a material having a specific gravity lower than the specificgravity of the material of the sprockets S₃ and S₄.

The annular mounting boss 44 a has a tubular configuration with aninternally splined surface that mates with the outer portion of thefreewheel 13 in a sliding, non-rotatable arrangement in a conventionalmanner. In the illustrated embodiment, the sprocket carrier C₂ includesfive circumferentially equally spaced attachment members 44 b to form asubstantially star-shaped configuration (not shown) similar to thesprocket carrier C₁. Each of the attachment members 44 b includes aninner end portion 45 a non-movably fixed with the mounting boss and anouter end portion 45 b spaced outwardly from the inner end portion 45 a.The attachment sections 40 e and 42 e of the sprockets S₃ and S₄ areattached to opposite axial sides of the outer end portions 45 b using aplurality of fasteners 46, such as rivets. The fasteners 46 can beidentical to the fasteners 36 or different from the fasteners 36. Theaxial length of the mounting boss 44 c and the axial position of theouter end portions 45 b are configured to cooperate with the freewheel13, the second sprocket carriers C₁ and C₃, the sprockets S₁-S₉ and thespacers T to provide optimum spacing, as mentioned above.

In this embodiment, the sprocket carrier C₂ includes a plurality ofspace maintaining projections 44 c extending axially towards theadjacent sprocket S₅. In particular, each of the each outer end portions45 b includes a space maintaining projection 44 c. In this embodiment,the space maintaining projections 44 c are integrally formed as aone-piece, unitary member with the attachment members 44 b of thesprocket carrier C₂. Each of the space maintaining projections 44 c hasa free end that is axially spaced from the adjacent sprocket S₅ by apredetermined spacing. Preferably, the predetermined spacing is 0.1millimeters or less. Of course, the predetermined spacing can be more orless as needed and/or desired. If the predetermined spacing becomes toolarge, then the amount of possible deflection of the sprockets S₃ and/orS₄ will become greater. Thus, it is preferable to keep the predeterminedspacing as small as possible. In fact, the predetermined spacing can bezero such that the free ends of the space maintaining projections 44 ccontact the sprocket S₅. In this embodiment, the free ends of the spacemaintaining projections 44 c are aligned with the fasteners, whichconnect the sprockets S₅ and S₆ to the sprocket carrier C₃. The spacemaintaining projections 44 c are located radially outwardly of theradially innermost end (the mounting boss 44 a) of the sprocket carrierC₂.

Referring now to FIGS. 2 and 27, the third sprocket subassembly, whichincludes the sprockets S₅ and S₆ mounted on an outer periphery of athird sprocket carrier C₃ will now be explained. The third sprocketsubassembly has a configuration similar to the second sprocketsubassembly, which includes the sprockets S₃ and S₄ mounted on an outerperiphery of a second sprocket carrier C₂. Specifically, the sprocketsS₅ and S₆ are conventional annular ring shaped sprockets similar to thesprockets S₃ and S₄, except for their size and number of teeth (e.g.,20T and 17T, respectively). Accordingly, the sprockets S₅ and S₆ willnot be explained and/or illustrated in detail herein for the sake ofbrevity. However, it will be apparent to those skilled in the art fromthis disclosure that the descriptions and illustrations of the sprocketsS₃ and S₄ also apply to the sprockets S₅ and S₆, except as explained andillustrated herein.

Similarly, the carrier C₃ is identical to the carrier C₂, except thatthe carrier has a smaller outer periphery so as to accommodate thesmaller sprockets S₅ and S₆ and the space maintaining projections 44 cof the sprocket carrier C₂ have been eliminated on the carrier C₃. Dueto the smaller diameter of the sprockets S₅ and S₆, deflection of thesesprockets is less likely than with the larger sprockets S₁-S₄. In anycase, the sprockets S₅ and S₆ are mounted to opposite axial sides of thethird sprocket carrier C₃ using a plurality of fasteners 46, such asrivets, in the manner identical to the manner in which the sprockets S₃and S₄ are attached to the second sprocket carrier C₂.

The sprockets S₁ and S₂ are mounted to the carrier C₁ before mountingthe sprocket carrier C₁ on the freewheel 13. Similarly, the sprockets S₃and S₄ are mounted to the carrier C₂ before mounting the sprocketcarrier C₂ on the freewheel 13 adjacent the carrier C₁, and thesprockets S₅ and S₆ are mounted to the sprocket carrier C₃ beforemounting the carrier C₃ on the freewheel 13 adjacent the carrier C₂. Inother words, the carrier C₁ is preferably mounted on the freewheel 13first, followed by the sprocket carrier C₂ and then the sprocket carrierC₃. After installing the sprocket carriers C₁-C₃ on the freewheel 13,the sprocket S₇, one of the spacers T, the sprocket S₈, the other spacerT and the sprocket S₉ can be installed onto the freewheel 13. At leastthe sprocket carriers the sprocket carriers C₁-C₃ and the sprocketsS₇-S₉ have internally splined mounting holes so as to be non-rotatablymounted on the freewheel 13. The spacers T can be internally splined,but do not have to be.

As shown in FIG. 2, the rear hub 11 is fastened to the rear fork of thebicycle frame 14. The freewheel 13 is disposed at one end of the rearhub 11. The freewheel 13 is conventional, and thus, will not beexplained and/or illustrated in detail herein. The freewheel 13basically includes an outer race or (tubular) ring 50, an inner race or(tubular) ring 52 and a one-way clutch 54 disposed between the inner andouter races 50 and 52. The outer race 50 has external splines extendingin a longitudinal direction parallel to the rotation axis X. The rearsprocket assembly 12 slides onto the splines of the outer race 50 suchthat the rear sprocket assembly 12 is non-rotatably mounted on the outerrace 50. A ring stopper 56 is thrreadedly mounted on the laterallyoutward end of the outer race 50 to retain the rear sprocket assembly 12on the outer race 50.

In understanding the scope of the present invention, as discussed above,the term “comprising” and its derivatives, as used herein, are intendedto be open ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “member” or “element” when used in thesingular can have the dual meaning of a single part or a plurality ofparts. Finally, terms of degree such as “substantially”, “about” and“approximately” as used herein mean a reasonable amount of deviation ofthe modified term such that the end result is not significantly changed.These terms of degree should be construed as including a deviation of atleast ±5% of the modified term if this deviation would not negate themeaning of the word it modifies.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents.

1. A bicycle rear sprocket assembly comprising: a sprocket carrierincluding at least one attachment member with an inner end portion andan outer end portion disposed radially outwardly of the inner endportion relative to a rotation axis of the sprocket carrier; a firstsprocket including a first attachment portion and a first chain engagingportion with a plurality of first teeth, the first sprocket beingdisposed on a first axial side of the attachment member; a secondsprocket including a second attachment portion and a second chainengaging portion with a plurality of second teeth that are fewer intotal number than a total number of the first teeth of the firstsprocket, the second sprocket being disposed on a second axial side ofthe attachment member; and a third sprocket including a third chainengaging portion with a plurality of third teeth that are fewer in totalnumber than a total number of the second teeth of the second sprocket,the third sprocket being disposed on a second axial side of the secondsprocket, the first and second attachment portions being attached to theouter end portion of the attachment member using a common fastener thatextends through the first and second attachment portions and the outerend portion of the attachment member, the second attachment portionhaving a free edge spaced radially inwardly from the common fastener bya distance at least as large as one-half of a maximum transversedimension of the fastener measured in a direction perpendicular to therotation axis, at least one of the attachment member, the secondsprocket and the third sprocket having at least one space maintainingprojection extending axially towards an adjacent one of the second andthird sprockets.
 2. The bicycle rear sprocket assembly according toclaim 1, wherein the free edge is spaced radially inwardly from thecommon fastener by a distance at least as large as the maximumtransverse dimension of the fastener measured in a directionperpendicular to the rotation axis.
 3. The bicycle rear sprocketassembly according to claim 2, wherein the free edge is spaced radiallyinwardly from the common fastener by a distance larger than a radialspace between the common fastener and a plurality of second roots of thesecond sprocket.
 4. The bicycle rear sprocket assembly according toclaim 1, wherein the outer end portion of the attachment member has afirst axially facing surface disposed on the first axial side with thefirst attachment portion opposed thereto and a second axially facingsurface disposed on the second axial side with the second attachmentportion opposed thereto, and the free edge of the second attachmentportion at least partially overlaps the second axially facing surface asviewed in a direction parallel to the rotation axis.
 5. The bicycle rearsprocket assembly according to claim 4, wherein the second attachmentportion contacts the second axially facing surface of the outer endportion of the attachment member.
 6. The bicycle rear sprocket assemblyaccording to claim 4, wherein the second attachment portion includes aradially inwardly extending tab with the free edge disposed at aradially inward most free end thereof.
 7. The bicycle rear sprocketassembly according to claim 6, wherein at least of majority of theradially inwardly extending tab overlaps the second axially facingsurface as viewed in a direction parallel to the rotation axis.
 8. Thebicycle rear sprocket assembly according to claim 6, wherein the atleast one space maintaining projection includes a pair of projectingsections extending from the second axially facing surface with the tabdisposed therebetween.